The program of research which is proposed in this document will cover two broad areas; field adaptation and orientation sensitivity in the turtle retina. Under the area of field adaptation, I propose to study: 1) What are the consequences of cone-cone coupling on cone-sensitivity? 2) What are the consequences of steady-state horizontal cell feed-back on cone sensitivity? Under the area of orientation sensitivity, I propose to investigate the consequences of the oriented receptive fields of the horizontal cells of the visual streak on more proximal retinal neurons. Do bipolar, amacrine and ganglion cells manifest oriented receptive fields? Is the dependence of the responses of these cells on slit orientation more sharply tuned than that seen in horizontal cells? Does the polarity of the bipolar cell response invert for particular slit orientations? Are there two classes of orientation sensitive ganglion cells; one sensitive to horizontal slits and another sensitive to vertical slits? Are there any morphological correlations which can be made with the oriented physiological findings. These problems will be pursued using standard intracellular electrophysiological techniques. The experiments on orientation sensitivity will be carried out using intracellular iontophoretic injections of either the fluorescent dye "Lucifer" or the electron dense dye "Horseradish Peroxidase." Gross anatomical studies will be performed on turtle retinas using the Golgi Collonier silver staining technique. All these techniques have become relatively easy to use and have been used with success by myself over the past few years.